This invention relates generally to irrigation control systems, and, more particularly, to digital systems for the control of a large number of irrigation or sprinkler valves in a desired sequence.
Large irrigation systems, whether used to irrigate agricultural property, sports facilities, or other types of property, include a number of water valves, which are typically solenoid-operated, and which must be opened and closed in a desired and controllable sequence as dictated by the terrain, climate and other factors. For relatively large systems, it is both costly and impractical to run a pair of wires from each of the valves back to a central controller. Accordingly, it is a principal objective in designing such systems to reduce the number of conductors between the central controller and the valve locations to an absolute minimum, i.e., ideally to two wires. Inherently, this objective requires the use of some form of control signal encoder at the central site, and control signal decoders at the valve locations.
Control systems utilizing a central encoder and a number of remote decoders connected to the encoder by only two wires, or by one wire and a ground return, are not unknown. However, such systems have heretofore utilized a technique in which device addresses and control signals are encoded in the form of relatively high-frequency signal bursts, and are then decoded by appropriate filtering at each of the decoders. For example, United States Patent No. 3,821,559, issued in the names of Ueda et al., discloses such a system for the digital control of a number of electrical devices in an automobile.
The present invention is concerned with significant improvements in a digital two-wire control system, of which the basic principles have been disclosed in a publication by one of the inventors. In accordance with these principles, power is transmitted over two wires from a central encoder to a number of decoders in the form of an alternating current. Control information in the form of decoder addresses and corresponding on/off codes is encoded onto the alternating-current signal by clipping portions thereof to indicate binary values of the digits to be transmitted as control information. At each decoder, the control information is decoded, and the alternating-current signal is rectified to provide power to operate valves under the control of the decoded information.
Although the aforementioned basic system provided a solution to the problem of minimizing the number of conductors from the central controller, it has two basic disadvantages in common with other systems of the prior art. First, there is no indication provided at the central site that commands transmitted to the decoders have been received. Second, there is no way of manually overriding the operations of the central controller from a field location, short of manually overriding the operation of each valve at its separate location. Manual control of the system from the field is highly desirable for a number of reasons, such as to permit temporary disabling of a valve for repairs, to permit application of extra water to a newly seeded area, or to permit termination of watering in a flooded area. The present invention is directed to improvements which overcome the aforementioned disadvantages.